BlueRidgeMark

Depends what you do with that power. Assuming everything is in proper working condition, the biggest variable is the loose nut behind the wheel.

If you want fuel economy, relax. Quit stomping the skinny pedal, stop tailgating, stop rushing up to red lights. Just chill out. You'll get there two minutes later than with all your stupid pushing and shoving your way through traffic.

Except on those days when you get there two minutes sooner, of course, because that happens, too.

Unless you are driving interstate distances, all the time that you gained by hot-rodding through traffic gets annihilated at the next red light, and you start at zero again. Then you do it all again. And again, your gains are zeroed out. Over and over again, and you never learn.


There was a thread a few years back that was very active for a few years. Yeah, years. It went on and on. It was all about getting better mileage, and no expense was spared. At the end, the guy who started it and kept it going, after all the mods he did, was getting exactly the same as I was getting in my box stock 97.

It's a brick, people, It's not going to get good mileage. Make sure everything is working correctly, and that's the best it's going to get. You are wasting your time chasing MPG.

ijeeep

OP's profile says he's from Oslo, Norway. Good chance the nut behind the wheel is properly adjusted. European driving style tends to be more flowing than ours. Not that crazy hyper-mileing crap that pisses off everyone around them, just more easier going on the gas with less quick starts and very few late hard stops like we see here.

There's a few guys cracked 24 mpg highway with the XJ after spending $600-1,000 or a few weekends worth of work. Anything above that is going to get real expensive real quick imho.

My box stock DD commuter & grocery getter XJ does that good on occasion. Box stock RWD with stick transmission,,for now.

97grand4.0

You missed the biggest easiest one of all. Fixing Jeep's misplaced IAT sensor. Get a 3/8 pipe thread plug. Remove the IAT from the manifold. Put in the plug. Drill a half inch hole in the air box and screw the IAT in it. Extend the wiring harness with some speaker wire and wire nuts or solder. Done.
Now your timing won't retard every time the engine gets hot.

ijeeep

IIRC Jeep moved the sensor to the air filter box in the Wrangler in 2004

97grand4.0

OP profile says 2000 XJ

NM-XJ

I'm extremely suspicious of this modification, to say the least. Posts from years ago (both here and NAXJA) indicate that increases in gas mileage are slim to nonexistent, as the O2 sensors in the exhaust flow are really the heavy hitters when it comes to mixture control.

Plus, I find the other claims of heat soak interference unsubstantiated. In my line of work, I regularly use probe-type thermocouples in extreme heat and cold-soaked environments. When fluid is flowing across the probe tip, the body temperature doesn't really matter and the probes accurately read the fluid temperature. It's only when you stop the flow (read: engine is turned off) that the probe tip temperature soaks to the surrounding environment. Admittedly that will prove to be a minor issue during startup, but the mass flow across the probe should be great enough that the transient period back to accurate fluid temperature reading is relatively short. And, finally, if the intake manifold does behave like a preheater, then it is more accurate anyway to measure the warmed intake air as it enters the cylinders...because that is what is actually going to get combusted.

I'd bet the reason people see an improvement from this mod are not the IAT location, but the fact that they clean the sensor when they change it's location.

Roler

HA, no. You obviously haven't driven around big european cities , especially Italian and the likes. Over 3 decades in Europe, I dare to challenge your claim. That said, Norwegians are of the reputation to be pretty decent on the roads tbo.
Just a side note to the thread
​​​​​

ijeeep

Yes driving in cities is lunge, parry, riposte. Get out of the cities and the drivers and driving are different matters, are they not ?
Der Autobahn and Greece are subjects all their own.

97grand4.0

If you're extremely suspicious, buy yourself a $19 scan tool and see the difference yourself.

RocketMouse

Yeah at the end of the day..... our old XJ's are about as aerodynamic as a 2 story house....
And I remember reading this years ago and believe it to be a true statement to this very day...... If you're looking to buy an old jeep and the phrase "fuel mileage" so much as even enters the conversation....then this is NOT the vehicle for you.
Us old jeep owners don't drive and mod these to get an extra mile per gallon.... it's to be able to successfully get them in and out of places that most other vehicles on the face of the planet couldn't even dream of going.

Dave51

Actually it makes no sense to me. Trick the engine into thinking it's colder than it is richens the fuel mixture, and contrary to the OP's goal.

Besides it's not like the engineers just pulled a sensor off the shelf and shoved it in the first hole they found. Unless evidence is presented that heat soak exists and inappropriately creates an adverse response to injector pulse length, AFAIC... it doesn't.

ijeeep

Jeep moved it to the air filter housing for the last two years of the 4.0. Why ? They don't make changes without reasons. What if the reason for that change is not fuel related but ignition timing related as stated in post #33 ?

ijeeep

Yes it does. That's why the mod was mentioned.

ijeeep

let's not forget, from all stock original to tube frame rock crawler, there's as many different reasons and purposes for owning an XJ as there are XJ owners.

The OP wasn't asking about the rediculous. He's trying to squeeze a few extra kilometers per 100 liters out of his tank in a land where gas is currently $7.15 a gallon.

Ralph77

I have been following this thread just out of curiosity.
As you guys know the '00 was a kinda running not really driveable purchase.
After I sorted through everything I turned my attention to seeing what I could do to improve MPG.
Do what I could and it is what it is.
So I figured my O2 sensors and fuel injectors had a 150K on them and needed to go.
I replace the injectors with brand new 4 hole ones.
I needed new tires and since she is just a DD went with some Cooper Discovery HT's in a 225 75 15.
I did read that thread on the other forum about the guy trying to achieve 25 MPG.
The one thing that I read in there and did was swap out my diff fluid to a synthetic.
Now I got kinda crappy mileage around town. Maybe 14 MPG.
But that made sense to me. 1/2 mile to work, when I am running errands it is short trips with multiple stops, etc.
Now I don't really think that my around town mileage improved.
And since I had not taken any longer highway trips yet had nothing to compare it to.
But if I take easy I do about 22 MPG on the highway. And I am OK with that cause that is what I really care about.
And as pointed out.
You are basically driving a billboard down the road so....... LOL.